I have a Scream out loud - 110dBA fixed tone Siren and I was wondering if anyone had used it as a ”alarm” speaker.
Can anyone help me with tips on how to use it?
All you have to do to activate that speaker is turn on its power. Even though it looks like it has an audio plug, it's not for an audio signal. If your siren comes with a power source, you could try finding a way to switch it on with the GPIO pins. Otherwise, you'll have to find your own power source and switch it on with the GPIO pins.
You can access the GPIO pins using the
wiringpi library from Gordon. They output 3.3V at a very low current, and are somewhat fragile. You will need to use transistors and/or relays as an interface. Googling either of those terms with "GPIO" should give you plenty of leads. The power supply for the siren should be 6-12V, and probably fairly robust. Do not expect the raspberrypi to power it in the least.
As for the alarm clock part, you will have to either set the clock on startup and never turn it off again, or find a way for it to resync the time when it powers up. There are a lot of questions on this and other sites on how to do that. Don't, however, expect your pi to power up when it needs to.
You can schedule your alarm using the at command, or the [cron](http://en.wikipedia.org/wiki/Cron] utility. Make a script that turns on your alarm, and schedule it for when you want to wake up... or when you want to scare your flatmates.
So that should be enough to get you started. I don't expect that you'll use it more than once, but good luck!